40 years of data show immigration decreases or stabilizes crime rates

When the number of immigrants goes up, violent crime goes down.

According to the White House Office of the Press Secretary, a recent Executive Order on Border Security and Immigration Enforcement
was intended to address the issue of “significant increase in violent
crime” due to immigration driven by “transnational criminal
organizations.” These claims directly contradict the results of academic
work on immigration and crime, and a recent study published in the Journal of Ethnicity in Criminal Justice reinforces that. It shows that immigration is not linked to increases in crime—in fact, this study suggests it's linked to reductions in certain types of crimes.
This study builds on previous findings on arrests and criminal
offenses. That previous data showed that foreign-born residents of the
US were less likely to commit crimes than native-born Americans. The new
study looked at 200 major metropolitan areas as defined by the US
Census Bureau. The researchers then used Census data and FBI crime
reporting data from 1970-2010 to look at trends for these regions.
The authors were interested in increases in crimes that might be
attributable to an influx of immigrants who decreased economic
opportunities or ended up in jobs that might otherwise have gone
to local-born residents. To that end, they looked at violent crimes and
property crimes, including rates of murder, non-negligent manslaughter,
aggravated assault, robbery, burglary, and larceny.
Looking across various times and locations, the researchers saw that
communities undergoing a demographic change due to immigration
clearly don’t experience significant increases in crime. In fact, even
though these communities may feel like they were in flux due to
population changes, crime was either stable or declined in communities
that were incorporating many immigrants.
The most striking finding comes from the authors’ models for violent
crime, murder, and robbery. The authors found that in three out of four
statistical models, an increase in the percentage of foreign-born
residents was significantly associated with decreases in these three
types of crimes. In other words, when immigrants went up, violent crime
went down. For example, rates of property crimes declined more rapidly
in cities with high percentages of foreign-born residents than they did
in cities with low percentages of foreign-born residents.

In summarizing this paper’s results, the lead author, Robert
Adelman (associate professor of sociology at University at Buffalo)
said, “the empirical evidence in this study and other related research
shows little support for the notion that more immigrants lead to more
crime.” Indeed, this study appears to show that for the last quarter of
the 20th century and the early portion of the 21st century, the presence
of immigrants was consistently associated with drops in violent and
property crimes in major US cities.